1. Field of the Invention
This invention relates to a method and an apparatus for displaying bitmap multi-color image data on a dot matrix-type display screen on which three primary color lamps consisting of light emitting diodes (LED) or the like are dispersedly arrayed, and more particularly, to a technology for realizing a full color display of high fineness and high quality.
2. The Prior Art
As one of typical examples, description will be made for a dot matrix-type LED full color display apparatus of 480 vertical lines and 128 horizontal dots. Each of the pixel lamps which are in total 61,440 pieces is an LED multi-color gathered lamp in which LEDs of three primary colors of RGB (red, green and blue) are densely arranged. Pixel data for activating one pixel lamp consists of 8 bits for each RGB, that is, 24 bit data in total, and is capable of full color expression of 16,777,216 colors. The image data for one screen is data of (61,440×24) bits.
In the case of a small display screen, the LED multi-color lamp is used, where each LED chip in RGB is molded in one lens body, and each of the LED multi-color lamps is evenly arranged, as one pixel lamp, in a matrix state on a screen. In the case of a large display screen, red LED lamps, green LED lamps and blue LED lamps that are molded respectively in a lens body are gathered in an appropriate number to constitute one LED multi-color gathered lamp, and the gathered lamps are evenly arranged one by one, as one pixel lamp, in a matrix state on a screen.
In both cases, in order to visualize an image on the screen, one piece of pixel data in the bitmap image data is allotted to one pixel lamp in a display screen, and the red lamp, the green lamp and the blue lamp in one pixel lamp are respectively activated to emit light according to red data, green data and blue data included in one piece of pixel data.
Recently, as blue LEDs having high luminance has been put into practical use, research and development concerning LED full-color displaying apparatuses of the dot matrix-type have started in full-scale. Former LED display apparatuses have dealt entirely with very simple images such as advertisement messages or guide messages constituted of characters and designs. Having passed such an era, recently, a variety of images, such as actually-filmed images or computer graphics images that are provided on an NTSC video signal used in a regular television broadcasting system or a VTR, or on a Hi-vision video signal, have become increasingly used. Image technology of a television broadcasting system has evolved significantly through a long history of research and development, and image expression performance of the NTSC video signal or the Hi-vision video signal have gone far beyond the expression capability of the current LED full color display apparatus. Therefore, demand for higher performance in the LED full color display apparatus has significantly increased.
Two approaches are conceived for making the LED full color display apparatus possess a higher performance. One is to increase an array density of the pixel lamps that constitute a display screen in order to improve resolution. The other is to devise an aspect of the image signal process such that the NTSC video signal or the Hi-vision video signal can be adapted to the LED full color display apparatus whose physical expression capability is difficult to be improved, without spoiling, to the furthest extent, the high image-expression ability of these signals.